The quality of a semiconductor material can considerably influence the performance of a solid-state device produced from said material. Solid-state devices can suffer from inferior lifetimes and operating characteristics when the semiconductor material has an undesirable density of crystal defects, for example dislocations. Such problems have hindered the development of semiconductors including gallium nitride (GaN), other Group III-nitrides (e.g., AlN, InN, GaInN) and other mixed nitrides (referred to herein as “III-nitrides”) as well as certain Group III-V compounds; and of certain other compound materials (e.g., IV, II-VI materials) generally. For many of these materials suitable and commercially useful growth substrates have limited availability and poor crystal quality. A suitable substrate closely matches the crystal properties of the target material to be grown; if these properties do not closely match, the resulting material usually has an unacceptable density of dislocations.
Specifically, in the case of GaN, crystal quality can be improved by pre-treatment of the growth substrates, e.g., by nitridization and other chemical modifications; by growing thin, low temperature buffer layers of other III nitrides, e.g., AlN or GaN, by thermal annealing, and the like. Methods such as epitaxial lateral overgrowth (ELO) and its variants (PENDEO, FIELO, etc) have proven successful in reducing dislocation density. However, these common methods often utilize lithographically produced masking elements that often produce materials with a non-uniform distribution of surface dislocations, undesirable in many applications. Some alternative methods of dislocation reduction for producing homogenous surface dislocation densities have utilized in-situ (or ex-situ) deposition methods to impede dislocation progression, in some instances with the addition of etchants to enhance surface dislocation dimensions. Examples of such impeding methods include US patent publication U.S. 2007/0259504, Tanaka et al. Japanese Journal of Applied Physics 39 L831 2000 and Zang et al. Journal of Applied Physics 101 093502 2007. Further alternative methods of dislocation reduction aim to limit dislocation propagation into the growing layer by, at an intermediate stage of growth of a GaN layer, enhancing defects present at the surface of the GaN layer by etching, then plugging plugging the enhanced surface defects with a masking material on which GaN does not readily nucleate, and then continuing GaN growth. Examples of such methods include US provisional patent application 61/127,720 filed May 14, 2008, which is incorporated herein by reference in its entirety.
Layers and crystals of III-nitrides of improved quality are desirable. Although applicable processes for doing so are available in the prior art and succeed to a certain degree in reducing the dislocation density in III-nitride materials, a method capable of producing greater dislocation reduction and uniformity of distribution is desirable.